Science —

Water: going, going, gone

Satellite data reveals that certain parts of India are using ground water at …

The availability of clean water is key to life, happiness, and prosperity. For those of us in the Western world, this is very nearly taken for granted—at least until you spend 3 days pulling up a well to mend a broken pump. However, this is the exception rather than the rule for much of the world's population.

When it comes to water resource management, things get tricky very quickly, as the "ownership" of water resources can be contentious. It is difficult to estimate the quantity and replenishment rate of underground aquifers, making portioning ground water challenging. Researchers have used satellite data to estimate ground water levels in 3 provinces in India, and found that the water level in those aquifers is falling.

The researchers focused on the Punjab, Rajasthan, and Haryana states (which include India's capital), where other research had indicated that ground water was beginning to run short. These states are classified as arid and semi-arid, and include part of the Thar desert. As a result, the population relies heavily on underground water for both irrigation and household uses. With 114 million people and a factor of three increase in the amount of irrigated land—that's the national average, by the way—the pressure on the Indus River plain aquifer has increased substantially.

To measure trends in the aquifer's level, the researchers used data from the Gravity Recovery and Climate Experiment (GRACE) satellite, which uses changes in the Earth's gravitational field to estimate the local density. From this, river levels, lake levels, ice mass, aquifer levels, and biomass changes can be estimated with reasonable mass accuracy. The reason that the researchers lumped the three states together is that the spatial resolution of GRACE is poor, coming in at about 160,000 square kilometers.

Using data from the years 2002 through to 2008, the researchers subtracted all the above-ground sources, leaving just the aquifer. They found that the aquifer was shrinking by an average of four centimeters per year, which corresponds to nearly 18 cubic kilometers of water per year. Having reached this conclusion, the researchers then looked at rainfall data and found that it had remained relatively close to average over the study period.

They also used a computer model of the aquifer to see if they could identify conditions that would replicate the data. This could only be achieved by ramping up irrigation and other human uses to levels beyond those that are sustainable.

Finally, they consider the possibility that they are actually seeing the results of glacial retreat instead of overuse. It turns out that if you totaled all the water lost to glacial retreat over the entire Himalayas for more than 40 years, it could account for about six percent of the water loss observed, allowing the researchers to discount that possibility.

The researchers urge caution in interpreting their work, because the time interval is too short to be certain of the long-term trends. Nevertheless, this data supports local measurements that also indicate that the aquifer is being emptied.

This data allows the authors to riff on the issue of water management. Consider the extent of the aquifer: it extends across three states in India and part of Pakistan. Can you imagine trying to get two national authorities, three or four state authorities, and numerous local municipalities to cooperate on a single water conservation strategy? Ultimately, conservation here will mean everyone losing access to a resource they've grown to consider theirs.

Now, of course, this data will add fuel to a debate over who gets what. This debate is taking place on the border of two nations that have nuclear weapons and a strong aversion to making nice with each other.

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Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He Lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com//Twitter@exMamaku